Dendritic cell-tumor coculturing vaccine can induce antitumor immunity through both NK and CTL interaction

Th1 polarization in the tumor microenvironment upregulates the myeloid-derived suppressor-like function of macrophages

Here, we investigated the effect of Th1 polarization in the tumor microenvironment (TME) on tumor-associated macrophage (TAM) maturation and activation. In our immunotherapy mouse model, with a Th1-dominant TME, tumors regressed in all cases, with complete regression in 80% of the cases. Monocyte-derived dendritic cells and activated CD4⁺ and CD8⁺T-cells increased in the tumor-draining lymph node, and correlated with each other in the therapeutic model. However, the cytotoxicity of tumor-infiltrating CD8⁺T-cells was slightly inhibited, whereas the number of T-cells significantly increased. Moreover, the number of TAMs increased; their maturation was inhibited; and nitrotyrosine (NT) production, as well as iNOS and arginase I expression, was increased, suggestive of the myeloid-derived suppressor cell-like immunosuppressive function of TAMs. IFN-γ knockout in the therapeutic model decreased NT production and induced macrophage maturation. Hence, Th1 polarization in the IFN-γ-dominant condition induces T-cell immune responses; however, it also enhances the immunosuppressive activity of TAMs.

Antitumoral Potency by Immunomodulation of Chloroform Extract from Leaves of Nitraria retusa, Tunisian Medicinal Plant, via its Major Compounds β-sitosterol and Palmitic Acid in BALB/c Mice Bearing Induced Tumor

This study evaluated the antitumoral effect of Chloroform extract from Nitraria retusa leaves, via its major compounds β-sitosterols and palmitic acid. BALB/c mice were subcutaneously inoculated with B16-F10 cells, then treated intra-peritoneally after 7 days with the chloroform extract for 21 days. They were then euthanized, and the tumors were weighed. Lung parenchyma was analyzed. Lymphocyte and macrophages proliferation, cytotoxic T lymphocyte (CTL) activities were evaluated using the MTT assay. Macrophage phagocytosis was evaluated by measuring the lysosomal activity and nitric oxide production. Antioxidant activity was studied by cellular antioxidant activity on macrophage and splenocytes and by lipid peroxidation inhibitory activity in liver cells, kidney, and serum. β-sitosterols and palmitic acid, major compounds of chloroform extract, impeded remarkably the expansion of the transplantable tumor, protected the lung parenchyma, and increased splenocytes proliferation and both CTL activities in tumor-bearing mice. β-sitosterols and palmitic acid were also seen to have enhanced lysosomal activity of host macrophages and antioxidant cellular activity. Also, they showed an inhibitory effect of lipid peroxidation. Our results suggest that antitumoral effect of β-sitosterols and palmitic acid from chloroform extract is related with its immunomodulatory activity, and opens the way for a nutrition application and coprocessing phytotherapy against cancer.

Neoepitopes as cancer immunotherapy targets: key challenges and opportunities

Over the last half century, it has become well established that cancers can elicit a host immune response that can target them with high specificity. Only within the last decade, with the advances in high-throughput gene sequencing and bioinformatics approaches, are we now on the forefront of harnessing the host's immune system to treat cancer. Recently, some strides have been taken toward understanding effective tumor-specific MHC I restricted epitopes or neoepitopes. However, many fundamental questions still remain to be addressed before this therapy can live up to its full clinical potential. In this review, we discuss the major hurdles that lie ahead and the work being done to address them.

Production of immunoregulatory polysaccharides from Crassostrea hongkongensis and their positive effects as a nutrition factor in modulating the effectiveness and toxicity of 5-FU chemotherapy in mice

Chemotherapy is generally accompanied by undesirable side effects, such as immunosuppression and malnutrition, which reduce tolerance to cancer therapies. Prior studies have shown that immunonutrition improves the clinical outcomes of cancer patients. In this study, immunoregulatory polysaccharides from Crassostrea hongkongensis were included in a nutrition formula that was administered to S180 tumor-bearing mice in combination with 5-fluorouracil (5-FU) treatment. The C30-60% fraction of the polysaccharides was characterized as a branched polysaccharide, with a high amount of d-glucose (96.76% of the total) and the highest uronic acid and sulfate groups' content among all of the polysaccharide fractions. The C30-60% polysaccharide fraction showed a maximal proliferative effect on RAW264.7 cells and T lymphocytes at a concentration of 0.0391 mg mL(-1) and 0.0781 mg mL(-1), respectively. Moreover, the combination treatment of the C30-60% polysaccharide-based nutrition formula (OPNF) with the administration of 5-FU effectively inhibited the growth of tumors and notably increased the leucocyte and lymphocyte counts in S180 tumor-bearing mice. In addition, a slight increase in the erythrocyte and hemoglobin values was observed in the mice treated with the combination of OPNF and 5-FU. These results suggest that supplementation with a C30-60%-based enteral formula would be beneficial for patients undergoing chemotherapy with 5-FU.

Oligoesculin fraction induces anti-tumor effects and promotes immune responses on B16-F10 mice melanoma

Laccase was used to enzymatically polymerize esculin. Oligoesculin fraction was obtained after ultrafiltration through a 5-kDa membrane. Several studies have been carried out to prove the effectiveness of natural substances such as immunomodulators to promote the anti-cancer activity in situ. The purpose of our report was to explore whether the anti-tumor potential of the oligoesculin fraction in vitro and in vivo is linked to its immunological mechanisms in melanoma-bearing mice. We revealed that oligoesculin fraction reduced B16-F10 proliferation and migration in vitro in a dose-related manner. Moreover, melanin synthesis and tyrosinase activity were inhibited in these melanoma cells in a concentration-dependent way. The anti-tumor potential of oligoesculin fraction was also assessed in vivo. Our results showed that intraperitoneal administration of oligoesculin fraction, at 50 mg/kg body weight (b.w.) for 21 days, reduced tumor size and weight with percentages of inhibition of 94 and 87 %, respectively. Oligoesculin fraction was effective in promoting lysosomal activity and nitric oxide (NO) production by peritoneal macrophages in tumor-implanted mice. In addition, the activities of natural killer (NK), cytotoxic T lymphocytes, and macrophages were significantly enhanced by oligoesculin fraction. These findings suggested that this polymer with its anti-tumor and immunomodulatory properties could be used for the treatment of melanoma.

Immunomodulatory and anticancer effects of Pituranthos tortuosus essential oil

Many studies have been performed to assess potential utility of natural products as immunomodulants to enhance antitumor activity in situ. In this study, an essential oil (EO) from the aerial parts of Pituranthos tortuosus was prepared using hydrodistillation, its composition was characterized, and its immunomodulatory potential was assessed. The results indicated that the EO contained sabinene, α-pinene, limonene, and terpinen-4-ol as major constituents. EO was also found to be able to significantly promote lipopolysaccharide (LPS)-stimulated splenocyte proliferation, suggestive of a potential for activation of B cells and enhanced humoral immune responses in hosts given this product. Effects of EO on cell proliferation and apoptosis were also investigated in B16F10 melanoma cells. EO-induced tumor cell growth inhibition was associated with characteristic apoptotic changes in the cells, including nuclear condensation. In conclusion, these data suggested to us that an EO of P. tortuosus could evolve to be a potential medicinal resource for use in the treatment of cancers.

Protection against cyclophosphamide-induced myelosuppression by ZPDC glycoprotein (24 kDa)

Immunomodulatory agents are often used to reduce myelosuppression and enhance immune response for cancer treatment. Cyclophosphamide (CTX) can induce oxidative stress in bone marrow resulting in suppression of anti-oxdiantive enzymes and causes myelosuppression. We isolated glycoprotein from Zanthoxylum piperitum DC fruit (ZPDC), and it consists of a carbohydrate (18%) and a protein (82%). The objective of this study was to investigate its protective activity against CTX-induced myelosuppression in Balb/c (n=6/group). The mice were orally administrated by ZPDC glycoprotein (10 and 20 mg/kg, BW) for 1 week in the presence or absence of CTX. Intracellular reactive oxygen species (ROS), anti-oxidant enzymes [superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT)], cyclin kinase inhibitors (CKIs: p53, p21 and p27), cyclin D1/ cyclin dependent kinase (CDK) 4, PCNA and cytokines [interleukin (IL)-3, and granulocyte⁄ macrophage-colony-stimulating factor (GM-CSF)] were evaluated using biochemical activity, Western blot analysis, and ELISA. The results obtained from this study showed that CTX decreased spleen and thymic indices, bone marrow cellularity and expression of cyclin D1/CDK4 and PCNA, but it increased CKIs, whereas ZPDC glycoprotein (20 mg/kg, BW) resulted in vice versa in CTX-induced Balb/c. Expression of IL-3 and GM-CSF were normalized by ZPDC glycoprotein. Thus, this study suggested that ZPDC glycoprotein prevents oxidative stress and myelosuppression in CTX-induced mice and might be a potential immunomodulatory agent.

NK cells: key to success of DC-based cancer vaccines?

The cytotoxic and regulatory antitumor functions of natural killer (NK) cells have become attractive targets for immunotherapy. Manipulation of specific NK cell functions and their reciprocal interactions with dendritic cells (DCs) might hold therapeutic promise. In this review, we focus on the engagement of NK cells in DC-based cancer vaccination strategies, providing a comprehensive overview of current in vivo experimental and clinical DC vaccination studies encompassing the monitoring of NK cells. From these studies, it is clear that NK cells play a key regulatory role in the generation of DC-induced antitumor immunity, favoring the concept that targeting both innate and adaptive immune mechanisms may synergistically promote clinical outcome. However, to date, DC vaccination trials are only infrequently accompanied by NK cell monitoring. Here, we discuss different strategies to improve DC vaccine preparations via exploitation of NK cells and provide a summary of relevant NK cell parameters for immune monitoring. We underscore that the design of DC-based cancer vaccines should include the evaluation of their NK cell stimulating potency both in the preclinical phase and in clinical trials.

Poly(ethylene glycol)-Lipid-Conjugated Antibodies Enhance Dendritic Cell Phagocytosis of Apoptotic Cancer Cells

A simple method for attaching immunoglobulin G (IgG) on the cell surface was successfully developed for enhancing phagocytosis of apoptotic tumor cells (ATCs) by dendritic cells (DCs) ex vivo. By conjugating with a poly(ethylene glycol) (PEG)-lipid, named the biocompatible anchor for the membrane (BAM), arbitrary IgG could be incorporated into the cell membrane. In particular, when IgG-BAM conjugates were prepared at the optimal molar ratio of IgG to BAM (1 to 20), almost all cells were efficiently modified with IgG by treatment with IgG-BAM. This simple method was successfully applied to four types of mammalian cells. Furthermore, treatment of ATCs with the IgG-BAM conjugate increased the phagocytosis ratio of ATCs by DCs two-fold when compared to no treatment. This phagocytosis-enhancing effect was nearly identical to treatment with a tumor-specific IgG. Thus, without employing the tumor-specific IgG, which is difficult to obtain for any tumor cells and is expensive, the present method could opsonize ATC with the use of arbitrary IgG. The results strongly indicate that IgG-BAM treatment represents a promising method for opsonizing ATC with human serum IgG, and that this approach will lead to objective clinical responses in DC vaccines.

Augmentation of cellular immune response by Ipomoea obscura and Ipobscurine alkaloid attenuates tumor growth in mice

The immune status of the host plays a crucial role in controling the process of carcinogenesis. General or selective activation of various immunocompetent cells and their secretory function to maintain a healthy immune status may help in cancer prophylaxis, as well as therapy. The present study focused on the effect of Ipomoea obscura and Ipobscurine on cell-mediated immune response. In this study we evaluated the effect of I. obscura and an indole alkaloid fraction from I. obscura on effector mechanisms of cell-mediated immune response by analyzing cytotoxic T lymphocyte (CTL) activity, natural killer (NK) cell activity, antibody-dependent cell-mediated cytotoxicity (ADCC), and antibody-dependent complement-mediated cytotoxicity (ACC). The effect of I. obscura and Ipobscurine on interleukin-2 (IL-2) and interferon-γ (IFN-γ) levels was also analyzed. In the in vitro and in vivo systems, I. obscura and Ipobscurine treatment augmented cell-mediated immune response by enhancing the killing activity of CTL and NK cells from splenocytes in normal as well as tumor-bearing mice. ADCC and ACC were also enhanced significantly in both normal and tumor-bearing animals after drug administration, compared with untreated control. Administration of I. obscura and Ipobscurine significantly enhanced the production of IL-2 and IFN-γ in normal as well as tumor-bearing animals. This study reveals that both I. obscura and Ipobscurine have the potential to augment immune response through the enhanced secretion of IL-2 and IFN-γ by T cells and thereby inhibit tumor growth and as an alternative medicine for cancer treatment.

Immunotherapy of MHC class I-deficient tumors

MHC class I downregulation is a general mechanism by which tumor cells can escape from T-cell-mediated immunity. This downregulation also represents a serious obstacle to the development of effective antitumor immunotherapy or vaccination. Therefore, successful immunotherapeutic and vaccination protocols should be optimized against tumors with distinct cell surface expression of the MHC class I molecules. Mechanisms leading to protective immunity may vary in different models with respect to the particular tumors (e.g., in their levels of residual expression of the MHC class I molecules on tumor cells or inducibility of MHC class I expression). Notably, both CD8+ cell-mediated immunity and MHC class I-unrestricted mechanisms can take place against MHC class I-deficient tumors. Since MHC class I downregulation is frequently reversible by cytokines and also by the activation of epigenetically silenced genes, an attractive strategy is to elicit specific cell-mediated immunity combined with restoration of MHC class I expression on tumor cells.

Immunomodulatory activity of butanol extract from Solanum lyratum in tumor-bearing mice

Solanum lyratum Thunb (Solanaceae) has been widely used for cancer as a folk remedy in Chinese traditional medicine. In this study, the main active fraction n-butanol extract from S. lyratum (BESL) was evaluated for the therapeutic efficacies on mice transplantable tumor and immunomodulatory potentials on the immune response in tumor-bearing mice. The effects of BESL on the growth of mouse transplantable S180 sarcoma, splenocyte proliferation, the activity of natural killer (NK) cells and cytotoxic T lymphocytes (CTL), production of cytokines from splenocytes, and serum antigen-specific antibody levels in S180-bearing mice were measured. BESL could not only significantly inhibit the growth of S180 sarcoma transplanted in mice, but also remarkably promote splenocytes proliferation, NK cell and CTL activity, interleukin-2 and interferon-γ production from splenocytes, and serum antigen-specific antibody levels in tumor-bearing mice (P < 0.05, P < 0.01, or P <0.001). The results suggested that BESL might exhibit antitumor activity by improving immune response, and it could act as antitumor agent with immunomodulatory activity. This study provided evidence to understand the therapeutic effects of S. lyratum for treatment of cancer and a natural product to further researches to be developed as a cancer chemopreventive agent.

Antitumor and immunomodulatory activity of polysaccharides from the roots of Actinidia eriantha

AIM OF THE STUDY

The roots of Actinidia eriantha Benth (Actinidiaceae) have been used for cancers in the Chinese folk medicine. The present study aimed at evaluating the antitumor potentials of the polysaccharides from the roots of Actinidia eriantha and elucidating their immunological mechanisms by determining the effects on the growth of tumor transplanted in mice and the immune response in tumor-bearing mice.

MATERIALS AND METHODS

The total polysaccharide AEP and fours purified polysaccharides AEPA, AEPB, AEPC and AEPD were isolated and purified from the roots of Actinidia eriantha by hot water extraction, ethanol precipitation, dialysis and gel filtration. Their effects on the growth of mouse transplantable tumor, splenocyte proliferation, the activity of natural killer (NK) cells and cytotoxic T lymphocytes (CTL), production of cytokines from splenocytes, and serum antigen-specific antibody levels in tumor-bearing mice were measured.

RESULTS

AEP and four purified polysaccharides could not only significantly inhibit the growth of mouse transplantable tumor, but also remarkably promote splenocytes proliferation, NK cell and CTL activity, IL-2 and IFN-gamma production from splenocytes, and serum antigen-specific antibody levels in tumor-bearing mice.

CONCLUSIONS

The antitumor activity of AEP and four purified polysaccharides might be achieved by improving immune response, and the composition of the monosaccharides, uronic acid contents and molecular weight could affect their antitumor and immunomodulatory activity.

Immunomodulatory and antitumor activity of triterpenoid fractions from the rhizomes of Astilbe chinensis

AIM OF THE STUDY

The objectives of this study were to evaluate the in vivo antitumor potential of the triterpenoid fraction from the rhizomes of Astilbe chinensis (Saxifragaceae) (Saxifragaceae) (ATF) and to elucidate its immunological mechanisms by determining its effects on the growth of mouse transplanted tumors and the immune response in naïve and tumor-bearing mice.

MATERIALS AND METHODS

The mice inoculated with mouse tumor cell lines were treated per os with ATF at the doses of 20, 40, 60 mg/kg for 10 days. The effects of ATF on the growth of transplantable tumor, splenocyte proliferation, the activity of natural killer (NK) cells, and production of interleukin-2 (IL-2) from splenocytes in tumor-bearing mice were measured. Meanwhile, the effects of ATF on 2,4-dinitrofluorobenzene (DNFB)-induced delayed type hypersensitivity (DTH) reaction and the sheep red blood cell (SRBC)-induced antibody response in naïve mice were also studied.

RESULTS

ATF could not only significantly inhibit the growth of mice transplantable tumor, but also remarkably increase splenocytes proliferation, NK cells activity, and the level of IL-2 secreted by splenocytes in tumor-bearing mice, promote the DTH reaction and enhance anti-SRBC antibody level in naïve mice, which indicated that the ATF could improve both specific and non-specific cellular and humoral immune response.

CONCLUSIONS

The antitumor activity of ATF might be achieved by improving immune response, and ATF could act as antitumor agent with immunomodulatory activity.

Quick Generation of Fully Mature Dendritic Cells From Monocytes With OK432, Low-Dose Prostanoid, and Interferon-?? as Potent Immune Enhancers

Dendritic cells (DCs) are one of the promising tools for enhancing antigen-specific immune responses in clinical settings. Many studies have been performed thus far to verify the efficacy of the DC vaccine in cancer patients; however, the responses have not always been satisfactory, partly because of DC incompetence. To obtain DCs potentially applicable for vaccination of cancer patients, our group sought to establish the strategy of DC generation mainly by modulating culture periods and maturation stimuli. Novel mature DCs that can be generated from monocytes within 3 days by using a combination of OK432 (Streptococcus pyogenes preparation), low-dose prostaglandin E2 (PGE2), and interferon-alpha (OPA-DCs) were developed. They strongly express CD83, CD86, and CCR7 and have potent ability to migrate to CCL21. In addition, they were able to activate natural killer and T helper 1 (TH1) cells and to induce peptide-antigen-specific cytotoxic T lymphocytes more significantly than monocyte-derived DCs stimulated with a conventional cytokine cocktail of tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-6, and PGE2 (monocyte-conditioned medium [MCM]-mimic DCs). The profound ability of OPA-DCs to stimulate these effectors is attributable to their higher expression of IL-12p70, IL-23, and IL-27 than MCM-mimic DCs, which was supported by the findings that the neutralization of IL-12p70 and IL-23 reduced the TH1 priming ability of OPA-DCs. Even when from advanced gastric or colonic cancer patients, OPA-DCs displayed abilities of migration and TH1 induction comparable to those from healthy subjects. Therefore, OPA-DCs may serve as a feasible vaccine with the potential to enhance TH1-dominant and cytolytic immune responses against cancers.

Dendritic Cells Pulsed with Total Tumor RNA for Activation NK-like T Cells Against Glioblastoma Multiforme

Dendritic cells (DCs) are potent antigen presenting cells and play critical role in T cell-mediated immunity. DCs have been shown to induce strong anti-tumor responses both in vitro and in vivo. Their efficacies in tumor therapy are being investigated in clinical trials. Previous evidence has shown that these DCs enhance the cytotoxicity of NK cells. We generated NK-like T cells (CD3(+)CD56(+)), a novel type of effector cells differentiated from normal lymphocyte, which is now being used for adoptive immunotherapy in clinical trials. This study aimed to elucidate the effects of NK-like T cells after co-culturing with DCs against tumor cells. The result revealed that tumor-derived RNA-pulsed DCs can enhance the immune responses of NK-like T cells against glioblastoma multiforme cell line but these effector cells did not appear to have the cytotoxic effect against normal cells (human umbilical vein endothelial cells (HUVEC) and fibroblasts) in vitro. This study may be beneficial for the development of new immunologic effector cells for using in adoptive immunotherapy for glioblastoma multiforme in the future.

Apolipoprotein A-I induces IL-10 and PGE2 production in human monocytes and inhibits dendritic cell differentiation and maturation

Apolipoprotein A-I (apoA-I), the major protein component of serum high-density lipoprotein, exhibits anti-inflammatory activity in atherosclerosis. In this study, we demonstrate that apoA-I inhibits DC differentiation and maturation. DC differentiated from monocytes in the presence of apoA-I showed a decreased expression of surface molecules such as CD1a, CD80, CD86, and HLA-DR. In addition, these DC exhibited decreased endocytic activity and weakened allogeneic T-cell activation. During DC differentiation in the presence of apoA-I, PGE(2) and IL-10, which are known to be DC differentiation inhibitors and/or modulators of DC function, were produced at remarkable rates, whereas IL-12 production in the cells after stimulation with CD40 mAb and IFN-gamma was significantly decreased in comparison with the control DC. T cells stimulated by apoA-I-pretreated DC produced significantly low levels of IFN-gamma, and apoA-I inhibited cross-talk between DC and NK cells, in terms of IL-12 and IFN-gamma production. Therefore, apoA-I appears to play an important role in modulating both innate immune response and inflammatory response. The novel inhibitory function of apoA-I on DC differentiation and function may facilitate the development of new therapeutic interventions in inflammatory diseases.

Administration of macrophage colony-stimulating factor mobilized both CD11b+CD11c+ cells and NK1.1+ cells into peripheral blood

We attempted the phenotypic characterization of peripheral blood (PB) cells after daily administration of macrophage colony-stimulating factor (M-CSF) in mice. The number of CD11b+ cells was increased by M-CSF treatment (2- and 5-day injections). Notably, CD11bbrightCD11cdim, CD11b+CD11c+ and CD11b+CD80+ cells were significantly increased by 2-day treatment of M-CSF. On the other hand, the number of NK1.1+ cells was not changed by the 2-day treatment, but it was significantly increased by the 5-day treatment. However, the numbers of CD3+ and NK1.1+CD3+ cells were not changed by M-CSF treatment. Then, mononuclear cells (MNCs) were separated from the PB of mice treated with saline or M-CSF, and they were incubated with GM-CSF + IL-4 or IL-2. Compared with the saline-treated one (S-MNCs), the MNCs of M-CSF-treated mice (M-MNCs) showed strong proliferation by the GM-CSF + IL-4 stimulation. The MNCs could stimulate proliferation of allo-T cells in the mixed lymphocyte reaction (MLR), especially the M-MNCs showed strong reaction. On the other hand, the stimulation by IL-2 induced strong cell growth of MNCs. And M-CSF treatment enhanced this response. Furthermore, the M-MNCs (stimulated by IL-2 in vitro) exhibited greater cytotoxicity against Yac-1 cells than the S-MNCs. In conclusion, we found that administration of M-CSF mobilized CD11b+, CD11b+CD11c+, CD11b+CD80+, and NK1.1+cells into PB. And the injection of M-CSF facilitates the generation of dendritic and natural killer cells from PB cells in vitro. These results suggest that the mobilized cells may provide for application of immunotherapy.

NK and CD8+ T cell-mediated eradication of poorly immunogenic B16-F10 melanoma by the combined action of IL-12 gene therapy and 4-1BB costimulation

In previous reports, systemic administration of a stimulatory monoclonal antibody directed against the 4-1BB receptor had no effect on survival or tumor burden in mice inoculated with the poorly immunogenic B16-F10 melanoma. We combined IL-12 gene transfer with 4-1BB costimulation to explore a previously noted cooperative anti-tumor effect against this model tumor. We hypothesize that the innate immune response mediated by IL-12-activated natural killer (NK) cells initiates the activation of the immune system, leading to the priming of T cells, whereas 4-1BB costimulation enhances the function of primed tumor-specific T cells. The effect of the combination therapy on the growth of subcutaneous (s.c.) tumors and pulmonary metastasis was examined. The combination therapy significantly retarded the growth of subcutaneously-inoculated tumors, and 50% of tumor-bearing mice survived with complete tumor regression. In contrast, neither IL-12 gene transfer nor anti-4-1BB antibody administration alone was as effective. Enhanced CTL activity against both B16-F10 tumor cells and TRP-2-pulsed EL4 syngeneic tumor cells was observed in tumor-bearing animals treated with the combination therapy 2 weeks after treatment and, in long-term survivors from this combination therapy, at >120 days. In a pulmonary metastatic model, only the combination therapy generated significant protection against metastasis. In vivo depletion of NK or CD8(+) but not CD4(+) subsets eliminated the protective immunity. Furthermore, NK cell depletion significantly reduced both tumor-specific CTL activity and the number of tumor-specific IFN-gamma-producing cells, suggesting that this synergistic effect requires the participation of both NK and CD8(+) T cells.